My 2 yr old son fell today and hit his head pretty hard, what are signs i should look for to be concerned about? is it ok for him to go to bed?

Concussion: Vomiting, fever, mental status (alertness, sleepiness, etc.). Concussion is something to worry. If he passed out when he fell, he had a concussion. Vomiting indicates high chance of concussion. Being lethargic means there may be a bleed in the brain. Being tired in the evening is probably fine as we do get tired. I would still take him to er to be on a safe side even if no obvious symptoms present.

Concerned: You have to check for vomiting, nauseas, visual changes, dizziness , near or not to syncope, headache, ..........Maintain awake for more than 3 to 5 hours, and call your pcp for check , or if the patient present any neulogical or anything you can go to er.